[haiku-3rdparty-dev] Re: Issue with drawing to BBitmap
- From: Elik Coreighn <elikcoreighn@xxxxxxxxx>
- To: haiku-3rdparty-dev@xxxxxxxxxxxxx
- Date: Sat, 10 Jul 2010 10:29:10 -0700 (PDT)
The debugger message already gives a hint. The short version: You must Lock()
the BBitmap before even adding the child view, and then Unlock() after
syncing and removing the view from the bitmap. The long version: BViews live
in a multi-threaded programming environment. To help the developer, there is
active debugging code in libbe.so BView code which checks for locking errors.
Effectively, any invokation of a BView method requires the BWindow that the
BView is part of to be locked. When a BView is added to a BBitmap, it is in
fact added to a "dummy" BWindow object owned by the BBitmap, which is used
for dispatching drawing commands to the app_server. This window, even though
the client thread never actually runs, still needs to be locked, since the
BView locking checks should not be even more complicated than they already
are. And of course the locking checks would still point out invalid
concurrent access in your client app, regardless of whether the client window
thread runs or not. To complete the picture about locking, perhaps the added
information that when you are running code in your window thread, the window
is always already locked, since you will always come from within the message
dispatching code, which locks the window.
Best regards,
-Stephan
Great explanation, thank you too, Stephan!
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